From your link: >Additionally, experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five- year period

From your link: >Additionally, experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five- year period due to advances in materials, designs, production methods and the standards. As a person who doesn't know a lot about motorcycling I found that surprising. Helmets seemed to me like an item the quality of which must have had plateaued a long time ago. But then again, you might naively think that about swimsuits.